System and method for estimating physical properties of objects and illuminants in a scene using modulated light emission

Abstract

Color balancing algorithms for digital image processing require an accurate estimate of the physical properties of the ambient scene illuminant, particularly its spectral power distribution. An active imaging method and apparatus estimate these properties by emitting modulated light with a known spectral power distribution into a region of a scene. Backscattered light is detected and demodulated to separate output representing active emitter light from output representing ambient illuminant light. Using the emitter-related detector output and the known emitter spectral power distribution, the surface spectral reflectance function of the illuminated scene region can be computed. Subsequently, the spectral power distribution of the ambient scene illuminant can be computed from the surface reflectance function and the illuminant-related output of the detector. The estimated spectral power distribution can be used in standard color balancing algorithms for digital or film images.